There can be lot's of reasons you aren't getting cold air. It could be fuses, belts, dirty filter, bad a/c copressor clutch, bad low pressure or high pressure swiitch, bad switch on dashcontrols, vacuum leak, etc.
If the refrigerant leaked out, though, you need to fix the leak.
Also, you don't just fill the system up with refrigerant. Overfilling can cause a burst hose or damage to the car. A burst hose will spray liquid refrigerant which will freeze anything it touches. We recently had a technician lose 2 fingers to a refrigerant leak incident. Freezing is similar in damage and pain to a burn from heat.
If liquid refrigerant gets in your eyes, it will blind you.
Damage to the car is easily fixed though.
Please be careful. Since you were unsure of how to tell the High Pressure side from the low pressure side, I assume you are not familiar with A/C systems.
I work for Carrier Air Conditioning as a Zone Engineer and have seen enough incidents when people who supposedly know what they are doing get seriously hurt.
it is easy to add refrigerant, but it can go wrong very quickly with serious consequences.
FWIW
So, if you insist on doing something dangerous, at least wear protective eye wear and insulated, nitrile gloves.
